Mark’s Nightmare Weather Pattern

TI think I mentioned earlier this spring that there is one weather pattern that I hate forecasting for…an upper level low sitting offshore with waves rotating out of it and into the Northwest.  2 reasons for that:  one is that models don’t handle the individual shortwaves well.  The other is that the periods of steady rain are usually quite short, followed by hours of sunshine if the onshore flow isn’t too strong.  So what starts out as a rainy day forecast could be wet until 8am, mostly sunny from 9am-4pm, then rain again after 5pm.  Viewers think we don’t know what we’re talking about and can’t forecast the weather…ugh!

What sticks out tonight is the good plume of moisture across the Eastern Pacific.  Models show precipitable water well above 1.20" the next 2 days as several waves move inland.  No big onshore push though until Friday, which leaves us increasingly warm & humid.  One wave moves into Wednesday evening, and another later Thursday/Friday AM.  With high freezing levels (10,000’+) and good subtropical moisture feed, we could get a good soaking.  Maybe .50"-1.00" in the lowlands.

As for the chances for thunder tomorrow & Thursday?  Tough one.  Our RPM (rapid update precision model) model here at the station seems to indicate some convection just ahead of the main line of rain tomorrow evening, and the same thing Thursday afternoon.  It’s tough because solid cloud cover (with surface cooling) ahead of both waves could cancel out the lifting effects of the approaching wave.  We’ll see.  Flow is southwest, which IS a similar setup to our convection about a week and a half ago.

14 Responses to Mark’s Nightmare Weather Pattern

  1. Derek Hodges says:

    dew points of near 60 right now, any sunshine tomorrow and those storms will rumble.

  2. Justin says:

    I remember the 31st of May well. The moisture was a bit spotty, but we had several tornadoes west of the mountains. PS, sorry for the length of the post.
    Event: Tornado
    Begin Date: 31 May 1997, 10:10:00 AM PST
    Begin Location: 1 Mile East of Keizer
    Begin LAT/LON: 44°59’N / 123°01’W
    End Date: 31 May 1997, 10:12:00 AM PST
    End Location: 3 Miles East South East of Keizer
    End LAT/LON: 44°59’N / 122°59’W
    Event: Tornado
    Begin Date: 31 May 1997, 02:15:00 PM PST
    Begin Location: Tacoma
    Begin LAT/LON: 47°14’N / 122°27’W
    End Date: 31 May 1997, 02:19:00 PM PST
    End Location: Tacoma
    End LAT/LON: 47°14’N / 122°27’W
    Length: 1 Mile
    Width: 0 Yards
    Magnitude: F1
    Fatalities: 0
    Injuries: 0
    Property Damage: $ 150.0K
    Crop Damage: $ 0.0
    State: Washington
    Map of Counties
    County: Pierce
    A weak tornado touched down in a south Tacoma neighborhood just east of I-5. A church suffered roof and beam damage and several trees were pushed over or snapped off. There were also some downed fences.
    Event: Tornado
    Begin Date: 31 May 1997, 04:45:00 PM PST
    Begin Location: Vancouver
    Begin LAT/LON: 45°38’N / 122°40’W
    End Date: 31 May 1997, 04:47:00 PM PST
    End Location: Vancouver
    End LAT/LON: 45°38’N / 122°40’W
    Length: 1 Mile
    Width: 20 Yards
    Magnitude: F0
    Fatalities: 0
    Injuries: 0
    Property Damage: $ 10.0K
    Crop Damage: $ 0.0
    State: Washington
    Map of Counties
    County: Clark
    A weak tornado briefly touched down in the Walnut Grove area of Vancouver, near I-205 and 4th Plain. A car was damaged, the roofing of a house was damaged, and a small shed was blown over.
    I remember seeing the storm that produced the Walnut Grove tornado, a fiarly nice rotating base on it and it passed right over my house. Tornado touched down about 10 minutes away from me.
    Length: 2 Miles
    Width: 50 Yards
    Magnitude: F0
    Fatalities: 0
    Injuries: 0
    Property Damage: $ 15.0K
    Crop Damage: $ 0.0
    State: Oregon
    Map of Counties
    County: Marion
    A tornado touched down near Chemawa Road and Highway 99 near Keizer at 1010 AM. Several people reported seeing the tornado on the ground for about 2 minutes. Three 30-40 foot tall trees were uprooted and a barn was damaged.
    Event: Tornado
    Begin Date: 01 Jun 1997, 11:37:00 AM PST
    Begin Location: 15 Miles West of Albany
    Begin LAT/LON: 44°38’N / 123°23’W
    End Date: 01 Jun 1997, 11:40:00 AM PST
    End Location: 14 Miles West North West of Albany
    End LAT/LON: 44°38’N / 123°22’W
    Length: 2 Miles
    Width: 25 Yards
    Magnitude: F0
    Fatalities: 0
    Injuries: 0
    Property Damage: $ 0.0
    Crop Damage: $ 0.0
    State: Oregon
    Map of Counties
    County: Benton
    A tornado was seen skipping along an unpopulated rural area 15 miles west of Albany by a pilot. No other information is available.

  3. Ryan says:

    I think it is just to emphasize that we probably won’t get showers but one good shot of rain during the day. As he mentioned before a upper level low is hard to predict and usually doesn’t cause a day-long rain event. But will usually give us at least 1 good rain shower during the day or a “Soaker.”
    Just how I’m digesting that one. 🙂

  4. Dmitri K says:

    I agree. I’ve never seen “a soaking” written before on Mark Nelsen’s forecast. I paused to think about it too. Maybe he’s trying to be different.

  5. CBC-Tech says:

    The seven-day struck me as odd. I notice “A Soaking” on the graphic yesterday, and still present today. How does this compare to “Heavy Rain”? Or does it? Am I over analizing this? LOL

  6. Ryan says:

    November? Heck I’ll be happy whe October rolls round and allergy season comes to an end. Time sure seems to be flying by this year. It seems like yesterday is was Janurary and were talking about snow.

  7. Ryan says:

    Looks like we have about 30 to 45 minutes of dry weather for anyone that wants to do something outside. Pretty impressive rain band just got into the Salem area and appears to be moving fast.

  8. hilsy says:

    No offense Mark, but whenever I here the words “upper level low” I tell people to not listen to the weather forecast. At least you back me up on this opinion. Now, can I get home in time to mow my lawn before the rain hits tonight?

  9. kirk says:

    5 months until November!!!! Lol

  10. Tyler says:

    Good point Dmitri…Actually May 31st, 1997 was the day we had a tornado up here in Vancouver, right around 5:30 pm
    . I remmeber it was only 1.5 miles from my house. I have pictures of the damage it did, nothing big, just tore up some trees, took down some fences and sheds etc.
    I also measured 0.88″ of rain that day.

  11. Ian says:

    what a wierd morning. we jumped about 15 degrees in 2 hours up here in longview. went out to get the paper at 9:30am and it was already up in the 60’s. feels good.

  12. Derek Hodges says:

    I suppose its possible. I noticed the severe weather outlook is watching eastern oregon.

  13. Dmitri K says:

    Kind of reminds me of a very similar pattern on in late May/early June 1997. It was very humid with warm overnight lows in the low 60’s, and heavy rain with morning thunderstorms here in the valley on May 31st. PDX had a record 1.45″ that day, one of the wettest days around this time of year we’ve ever had.
    Later that day the activity moved north and east and lead to a severe weather outbreak in eastern Washington. If I remember correctly it produced the biggest tornado outbreak in Washington state history, with 6 or 7 confirmed tornadoes from around Moses Lake to Spokane.
    Then on June 1st we had a funnel cloud touch down in the valley (around Salem I believe) which prompted a tornado warning there.
    Could we see something similar develop this time?

  14. alex says:


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